Process of manufacture of temperaturesensitive recording paper



Feb. 6, 1962 D. F. A. MOHNHAUPT 3,020,172

PROCESS OF MANUFACTURE OF TEMPERATURE-SENSITIVE RECORDING PAPER Filed Sept. 8, 1959 t i POLYMERIC LOW BF. #1 SUBSTANCE SOLVENT A l Bl SOLUTION 'A IN "5 INERT ORGANIC LIQUID lc" MiXTURE A/B B c l APPLICATON JLEVAPoRATmN IILEVAPORATION OF MIXTURE OF SOLVENT OFINERT LIQUID INVENTO/P D/ETR/CH [-7 A. MOHNHAUPT United States Patent O 3,020,172 PROCESS OF MANUFACTURE OF TEMPERATURE- SENSITIVE RECORDING PAPER Dietrich Fritz Arthur Mohnhaupt, Vesenaz, Switzerland,

assignor to Permaco S.A., Vesenaz, Switzerland, a corporation of Switzerland Filed Sept. 8, 1959, Ser. No. 338,401

Claims priority, application Switzerland Sept. 16, 1958 26 Claims. (Cl. 117-363) of an organic highly polymerized material which is applied in the form of a solution or dispersion to the dark carrying paper. On simply drying the solution or dispersion which is applied, a white layer is not directly formed,

but in general a lacquer-like coating, through which the dark background is visible. This coating was hitherto caused to become white by conducting a strong current of cold air over the liquid layer on the paper. Owing to the rapid evaporation of the solvent caused thereby, the cold due to theevaporation produces effects which cause moisture in the airto be deposited on the layer and partly in the interior thereof. The whitening produced in this manner is not uniform and is dependent on many chance eifects.

A second method of producing the whitening is based on the formation of very many very small hollow spaces in the interior of the layer during the evaporation of the solvent. These hollow spaces are only formed when the solvent is evaporated sufiiciently rapidly before the solid constituents of the layer become coagulated. For this reason only very dilute solvents with a solid content up to approximately 6 percent by weight can be used, because.

the solid highly polymerized constituents of the layer possess the property of tenaciously retaining the solvent.

does not otter any appreciable resistance tothe current of air. On continued drying the layer can break at the troughs of the'waves, or in any casethethickness of the layer is not uniform. i

The present. invention obviates these disadvantages and I is inert towards paper and in which the above-mentioned substance is insoluble, the higher boiling liquid being added in an amount such that the highly polymerized substance is not precipitated andfthe total mixture (C-l-A/B) has a'solid content of 6 to 20 percent by weight. A dark carrying paper P is then coated (step I in the accompanyingfiowsheet) with a layer of this mixture and first the low boiling solvent (B; step II) According to the invention, the process for 3,020,172 "Patented Feb. 6, 1962 2 and after this the higher boiling liquid (C; step 111) is evaporated.

The highly, polymerized organic substance which forms the coating layer is dissolved in a low boiling point solvent, for example, acetone, methylacetate, tetrahydrofuran, dimethylacetal, or methylenechloride. As much of the higher boiling organic liquid, in which the substance which forms the layer is insoluble, is added so as not to cause precipitation of the substance. After application to the carrying paper the solvent is mainly evaporated, so that the substance which forms the coating layer is precipitated' as a finely divided light-colored precipitate in the organic liquid. On continued evaporation of the organic liquid, the substance which forms the coating layer combines intimately with the surface of the carrying paper, an extremely good adherence being obtained.

, The whitening of the layer depends therefore on the precipitation of very small particles of solid deposited at random in an indifferent liquid.

The time of evaporation of the solvent should be between l.8 and 24, preferably 2, that of the organic liquid, should be between 2.8 and 4, preferably 3,as compared withthat of diethylether which is taken to be equal to l.

The indilierent organic liquid should have no chemical atiinity for the constituents of the carrying paper because experiments have shown that otherwise distortion and shrinking of the carrying paper occur, whereby the adherence of the temperature-sensitive layer considerably decreases. Liquids which are not usefulare, for example, substances having OH-groups. (alcohols and acids). In

' particular no water should be present. Substances which can be used with advantage are aliphatic hydrocarbons, for example, cyclohexane, hexane, heptane, benzine and the like.

As the substances which form the coating layer, all highly polymerized organic substances are suitable, provided they are soluble in the above-mentioned solvents and insoluble in the above-mentioned liquids and possess a satisfactory white shade or color and have, either in the pure form or in mixtures, a melting or sintering point which is between C. and 220 C. Suitable substances are for example cellulose esters, cellulose ethers, polystyrene, polyvinylacetate, ketone resins, derivatives'of colophony, phenol-formaldehyde resins, polyvinylchloride, polyvinylidenechloride, polymethacrylate, resins, etc.

' Since the concentration of the layer forming substance in the present process amounts to 6'to 20% and is preferably 10%, the solution has a viscosity which is comparablewith that of glycerine. Owing to this, the formation of waves and cracks on drying with air is prevented-and a layer of uniform thickness is formed.

As previously mentioned a mixture of high polymerizedsubstances may be used as the substance which forms the coating layer. By altering the composition of the mixture a suitable melting point for the mixture, which is adapted tosuit the requirements of the recording apparatus, can be obtained. Also by addition of low melting point waxes or resins and softeners the melting point of the layer can be adjusted as desired.

The whitening of the layer can be accelerated by removing the solvent by meansof a current of air at a temperature of about 35 C. instead of with a current of cold air. After this, the higher boiling organic liquid can be evaporated by a current of hot air, the temperature of which is below the melting temperature of the solid constituents forming the coating layer. Therefore a current of air at a temperature of 20 to 40 C., pref erably 35 C., is first directed on to the layer until this appears white and after this a current of air at a temperature of 40 to 100 C., preferably 75 C., is directed on the layer until the higher boiling liquid is completely evaporated.

An advantageous process in accordance with the invention is, for example, to use polyisobutylene as the highly polymerized substance and pentane, hexane or benzine as the lower boiling solvent, and ethylacetate or methylethylketone as the higher boiling organic liquid.

There is a limit to the speed with which the values to be registered can be recorded. This is reached when the amount of heat transmitted from the stylus to the temperature-sensitive coating layer is no longer sufficient to cause the layer to become transparent. The coating layers produced by the methods of the invention can be caused to respond in a considerably shorter time if two additional precautions are used either singly or in combination; these enable the time of response of the paper to be reduced by about two orders of magnitude.

The first precaution enables the thickness of the temperature-sensitive layer to be reduced without detracting from the degree of whiteness. For this purpose there is added to the solid constituents of the coating layer an optical brightener which has the property of causing a grey surface to appear white. A temperature-sensitive layer made by the process described cannot be made thinner than 15' to 1 Without the dark background appearing through it. However, if a small amount of an optical brightener is added, the thickness of the layer can be reduced to 5 1 while maintaining the necessary degree of whiteness. with a layer having a thickness of a is reduced by about three times.

Optical brighteners are known in the textile industry. They are frequently used in order to cause textiles which have frequently been washed and have a grey appearance to appear white again. For the purposes of the present invention there may be used derivatives of benzthiazole, stilbene and triazine (see British Patent No. 683,895, Swiss Patent No. 275,140 and Belgian Patent No. 540,323) which are known in commerce under the registered trademark Blankophor of Farbenfabriken B. yer A.G., and are used as optical brighteners.

The second additional precaution is based on the idea of producing the heat necessary for making the layer transparent by exothermic chemical reaction in the layer itself, the stylus requiring only to be heated to the reaction temperature at the place of contact. Suitable reactions which evolve the necessary heat are oxidation and neutralization processes. For the present purpose it is advantageous if the speed of the chemical reaction increases greatly with rise of temperature. Solid substances in general react with one another only extremely slowly, whereas they can react very rapidly at temperatures above their melting points.

Strong oxidizing agents, such as peroxides, for example, are often very stable in the solid state and at room temperature whereas they decompose very rapidly at the temperature of their melting point and slightly above this temperature. In the presence of a reducing agent they evolve atomic oxygen which liberates more heat on oxidation than molecular oxygen. If peroxy acids are used in the presence of bases having a reducing action, for example certain amines, the neutralization also acts as an additional supplier of heat of 13.7 kcal./mol.

When the hot stylus makes a superficial contact for a short time with the coating layer, the nearest part of the layer melts, which part contains in addition to the highly polymerized organic substance, the peroxy acid (or an inorganic peroxy acid) and a reducing amine R'NH (or a suitable inorganic compound) and in The time of response as compared "3 some cases also an optical brightener. The reactions which then take place are substantially as follows:

RONH2+RC 0 OH=(RIONH3)+(RC o 0)+13.7 kcaL/mol. The heat produced is sufiicient to allow the layer to melt or become glazed down to the dark background. There is thus formed a visible writing trace where the layer without the chemical reactions would be only quite superficially melted.

It is advantageous to use substances, the reaction products of which remain liquid at the reaction temperature, that is to say at a temperature of about 100 C., in order to save energy which must be expended in melting the substances.

By altering the nature and concentration of the oxidizing and reducing agents the time of response of the layer can be considerably varied. The concentrations, however, must not be so high that spontaneous reactions occur.

By suitable combination of the process of the invention with the two precautions described above record papers can be made which have a time of response of from 2.5 to 0.1 milliseconds, whereas the hitherto known record papers had a time of response of above 10 milliseconds.

The invention will now be explained in greater detail with the aid of the following examples.

Example 1 16.5 g. of celluloseaceto-butyrate and 0.8 g. of phthalic acid dicyclohexylester are dissolved in 120 g. of acetone. 80 g. of cyclohexane are then added with stirring. This mixture is applied in a thickness of 0.05 mm. to a black carrying paper by means of rollers, and is blown for 10 seconds with air at a temperature of 35 C. and then for 10 seconds with air at C. The layer obtained responds at a temperature of about 120 C.

Example 2 11 g. of celluloseaceto-butyrate and 11 g. of ethyl cellulose are dissolved in 100 g. of tetrahydro furan and then 100 g. of benzine having a. boiling range of to C. are added while stirring. The further treatment is the same as in Example 1. The white layer obtained responds at a temperature of approximately C.

Example 3 20 g. of polystyrene and 2.2 g. of a ketone res-in (made from cyclohexanone and methylcyclohexanone) are dissolved in 120 g. of methylacetate. Then 80 g. of heptane are added while stirring. The application and drying of the coating takes place as in Example 1. The layer obtained responds at a temperature of about 100 C.

Example 4 22 g. of polyisobutylene (molecular weight about 200,000) are dissolved in 110 g. of hexane. 90 g. of ethylacetate are then added with stirring. The further treatment takes place as in Example 1. The layer obtained responds at a temperature of about C.

Example 5 5 Example 6 14 g. of celluloseaceto-butyrate, 0.7 g. of phthalic aciddicyclohexylester, 1.6 g. of nionoperoxyphthalic acid and 1 g. of meta-aminophenol are dissolved in 120 g. of acetone. Then 80 g. of 'cyclohexane are added with stirring. The further treatment is the same as in Example 1. The layer obtained has a time of response of only 0.25 milliseconds on contact with a stylus heated to 220 C.

Example 7 2.6 mg. of. an optical brightener (Blankophor) are added to the solution obtained in Example 6. The layer is applied in the same way as in Example 1 and base. thickness of about 5 to 8p. The time or response is from 0.1 to 0.18 millisecond.

Example 8 18 g. of polystyrene, 2 g. of a ketone resin (made from cyclohexanone and methylcyclohexanone), 0.65 g. of dibenzoylperoxide and 1.5g. of N-dimethyl-meta-aminophenol are dissolved in 120 g. of methylacetate. After addition of 80 g. of heptane the layer is applied to black paper as in Example 1.

Example 9 1.5 mg. of optical brightener (Blankophor) are added to the mixture described in Example 8 and the mixture is applied to black paper in the manner described in Example 1, the layer having a thickness of to 8a. This has a time of response of 0.1 to 0.15 millisecond on contact with a stylus heated to 220 C.

What I claim is:

1. A process for manufacturing temperature-sensitive recording paper having a light-colored coating layer on a dark carrier paper base, comprising admixing with the solution of a polymerized organic substance having a sintering point of from about 80 to 220 C. in an organic solvent therefor having a boiling point lower than the sintering point of said polymerized material, an organic liquid free from hydroxyl groups which has a boiling point above the boiling point of said organic solvent and below the sintering point of said polymeric material, which is inert toward said paper base, and in which said polymerized material is insoluble, said liquid being added in such amounts to said solution that said polymerized material is not precipitated therefrom, and that the solids content of the resulting mixture is from about 6 to 20% by weight; applying said resulting mixture on said paper base; heating the resulting layer of said mixture on said paper base to evaporate substantially exclusively said solvent therefrom, thereby forming a finely divided gray to white precipitate of said polymerized substance in said inert liquid on said paper base; and then heating further to such temperature as to evaporate said inert liquid therefrom and forming a gray to white coating of said polymerized substance on said paper base.

2. The process as described in claim 1, wherein said resulting mixture is applied on said paper base in such amount that the final gray to white coating of said polyrnerized substance on said paper base has a thickness of at least 10 microns to microns and more.

3. The process described in claim 1, wherein said polymerized organic substance is selected from the group consisting of cellulose esters, cellulose ethers, polystyrene, polyvinylacetate, ketone resins, colophony derivatives, formaldehyde resins, polyvinylidene chloride, polyvinyl chloride, polymethacrylate, coumarone' resins and polyacetone, methylacetate, tetrahydrofuran, dimethylacetal and methylenechloride, and the higher boiling organic liquid is selected from the group consisting of cyclohexane, hexane, heptane and benzine.

6. A process according to claim 1, wherein the low boiling solvent is selected from the group consisting of pentane and hexane, and the higher boiling organic liquid is selected from the group consisting of ethylacetate and ethyl ethyl ketone, and the polymerized organic substance is polyisobutylene.

7. A process for manufacturing temperature-sensitive recording paper having a light-colored coating layer on a dark carrier paper base, comprising admixing with the solution of a polymerized organic substance having a sintering point of from about 80 to 220 C. in an organic solvent therefor having a boiling point lower than the sintering point of said polymerized material, an organicliquid free from hydroxyl groups which has a boiling point above the boiling point of said organic solvent and below the sintering point of said polymeric material, which is inert toward said paper base, and in which said polymerized material is insoluble, said liquid being added in such amounts to said solution that said polymerized material is not precipitated therefrom, and that the solids content of the resulting mixture is from about 6 to 20% by weight; applying said resulting mixture on said paper base; directing a current of air at a temperature of from about 20 to 40 C. on to the surface of the resulting layer of said mixture on said paper base to evaporate substantially exclusively said solvent therefrom, until said layer iswhitened thereby forming a. finely divided prccipitate of said polymerized substance in said inert liquid on said paper base; and then directing another current of air at a temperature of from about 40 to 100 C. on

to the surface of the resulting layer on said paper base,

thereby evaporating said inert liquid therefrom and forming a gray to white coating of said polymerized substance on said paper base.

8. A process for manufacturing temperature-sensitive recording paper having a light-colored coating layer on a dark carrier paper base, comprising admixing with the solution of a polymerized organic substance having a sintering point of from about 80 to- 220 C. and an optical brightener in an organic solvent therefor having a boiling point lower than the sintering point of said polymerized material, an organic liquidfree from hydroxyl groups which has a boiling pointabovc the boiling point of said organic solvent and below the sintering point of said polymeric material, which is inert toward said paper base, and in which said polymerized material is insoluble, said liquid being added in such amounts to said solution that said polymerized material is not me cipitated therefrom, and that the solids content of the resulting mixture is from about 6 to 20% by weight; applying said resulting mixture on said paper base; heating the resulting layer of said mixture on said paper base to evaporate substantially exclusively said solvent therefrom, thereby forming a finely divided gray to White precipitate of said polymerized substance in said inert liquid on said paper base; and then heating further to such temperature as toevaporate said inert liquid therefrom and forming a gray to white coating of said polymerized substance on said paper base.

9. The process described in claim 8, wherein the optical brightener is selected from the group consisting of benzthiazole Optical brighteners, stilbene optical brighteners and triazine optical brighteners.

p 10. A process for manufacturing temperature-sensitive recording paper having a light-colored coating layer on a dark carrier paper base, comprising admixing with the solution of a polymerized organic substance having a sintering point of from about to 220 C. in an organic solvent therefor having a boiling point lower than the sintering point of said polymerized material, an oxidizing agent selected from the group consisting of acid peroxides and peroxyacids, a reducing amine capable of reacting with said oxidizing agent at temperature above their melting points, with evolution of heat, and an organic liquid free from hydroxyl groups which has a boiling point above the boiling point of said organic solvent and below the sintexing point of said polymeric material, which is inert toward said paper base, and in which said polymerized material is insoluble, said liquid being added in such amounts to said solution. that said polymerized material is not precipitated therefrom, and that the solids content of the resulting mixture is from about 6 to 20% by weight; applying said resulting mixture on said paper base; heating the resulting layer of said mixture on said paper base to evaporate substantially exclusively said solvent therefrom, thereby forming a finely divided gray to white precipitate of said polymerized substance in said inert liquid on said paper base; and then heating further to such temperature as to evaporate said inert liquid therefrom and forming a gray to white coating of said polymerized substance on said paper base.

ll. The process described in claim 10, wherein said oxidizing agent is monoperoxyphthalic acid and said reducing amine is meta-aminophenol.

12. The process described in claim 10, wherein said oxidizing agent is dibenzoylperoxide and said reducing amine is N-dimethyl-meta-aminophenol.

13. A process for manufacturing temperature-sensitive recording paper having a light-colored coating layer on a dark carrier paper base, comprising admixing with the solution of a polymerized organic substance having a sintering point of from about 89 to 220 C., an optical brightener, and an oxidizing agent selected from the group consisting of acid peroxides and peroxyacids, and a re ducing amine capable of reacting with said oxidizing agent at a temperature above their melting points with evolution of heat in an organic solvent therefor having a boiling point lower than the sintering point of said polymerized material, organic liquid free from bydroxyl groups which has a boiling point above the boiling point of said organic solvent and below the sintering point of said polymeric material, which is inert toward said paper base, and in which said polymerized material is insoluble, said liquid being added in such amounts to said solution that said polymerized material is not precipitated therefrom, and that the solids content of the resulting mixture is from about 6 to 20% by weight; applying said resulting mixture on. said paper base; heating the resulting layer of said mixture on said paper base to evaporate substantially exclusively said solvent therefrom, thereby forming a finely divided gray to white precipitate of said polymerized substance in said inert liquid on said paper base; and then heating further to such temperature as to evaporate said inert liquid therefrom and forming a gray to white coating of said polymerized substance on said paper base.

14. The process described in claim 13, wherein said optical brightener, said oxidizing agent and said amine are not insoluble in said organic liquid.

15. A coating bath for the manufacture of temperaturesensitive recording paper, consisting essentially of a solution of a polymerized organic substance having a sintering point of from about 80 to 220 C. in an organic solvent therefor having a boiling point lower than the sintering point of said polymerized material, and an organic liquid free from hydroxyl groups which has a boiling point above the boiling point of said organic solvent and below the sintering point of said polymeric material, which is inert toward said paper base, and in which said polymerized material is insoluble, said liquid being contained in such amounts in said solution. that said polymerized material is not precipitated therefrom, and that the solids content of the resulting mixture is from about 6 to 20% by weight.

16. The coating bath described in claim 15, wherein said polymerized organic substance is selected from the 8 group consisting of cellulose esters, cellulose ethcrs, polystyrene, polyvinylacetate, ketone resins, colophony derivatives, formaldehyde resins, polyvinylidene chloride, polyvinyl chloride, polymethacrylate, coumarone resins and polyisobutylene.

17. The coating bath according to claim 15, wherein the low boiling solvent is selected from the group consisting of acetone, methylacetate, tetrahydrofuran, dimethylacetal and methylcnechloride, and the higher boiling organic liquid is selected from the group consisting of cyclohexane, hexane, heptane and benzine.

18. The coating bath according to claim 15, wherein the low boiling solvent is selected from the group consisting of pentane and hexane, and the higher boiling organic liquid is selected from the group consisting of ethylacetate and methyl ethyl ketone, and the polymerized organic substance is polyisobutylene.

19. A coating bath for the manufacture of temperaturesensitive recording paper, consisting essentially of a solu tion of a polymerized organic substance having a sintering point of from about to 220 C. and an optical brightener in an organic solvent therefor having a boiling point lower than the sintering point of said polymerized material, and an organic liquid free from hydroxyl groups which has a boiling point above the boiling point of said organic solvent and below the sintering point of said polymeric material, which is inert toward said paper base, and in which said polymerized material is insoluble, said liquid being contained in such amounts in said solution that said polymerized material is not precipitated therefrom, and that the solids content of the resulting mixture is from about 6 to 20% by Weight.

20. A coating bath for the manufacture of temperaturescnsitive recording paper, consisting essentially of a solution of a polymerized organic substance having a sistering point of from about 80 to 220 C., an oxidizing agent selected from the group consisting of acid peroxides and peroxyacids, and a reducing amine capable of reacting with said oxidizing agent at a temperature above their melting points with evolution of heat in an organic solvent therefor having a boiling point lower than the sintering point of said polymerized material, and an organic liquid free from hydroxyl groups which has a boiling point above the boiling point of said organic solvent and below the sintering point of said polymeric material, which is inert toward said paper base, and in which said polymerized material is insoluble, said liquid being contained in such amounts in said solution that said polymerized material is not precipitated therefrom, and that the solids content of the resulting mixture is from about 6 to 20% by Weight.

21. A coating bath for the manufacture of temperaturesensitive recording paper, consisting essentially of a solution of a polymerized organic substance having a sintering point of from about 80 to 220 C., an optical brightener, and an oxidizing agent selected from the group consisting of acid peroxides and peroxyacids, and a reducing amine capable of reacting with said oxidizing agent at a temperature above their melting points with evolution of heat in an organic solvent therefor having a boiling point lower than the sintering point of said polymerized material, and an organic liquid free from hydroxyl groups which has a boiling point above the boiling point of said organic solvent and below the sintering point of said polymeric material, which is inert toward said paper base, and in which said polymerized material is insoluble, said liquid being contained in such amounts in said solution that said polymerized material is not precipitated therefrom, and that the solids content of the resulting mixture is from about 6 to 20% by weight.

22. A temperature-sensitive recording paper consisting essentially of a dark carrier paper base and a coating thereon of a finely divided gray to white precipitate of a polymerized organic substance having a sintering point of from about 80 to 220 C.; said coating having a thickness of at least about 10 to 15 microns, and being 9 formed from a layer of a mixture of the solution of said polymerized organic substance in an organic solvent therefor having a boiling point lower than the sintering point of said polymerized material, with an organic liquid tree from hydroxyl groups which has a boiling point above the boiling point of said organic solvent and below the sintering point of said polymeric material, which is inert toward said paper base, and in which said polymerized material is insoluble, said liquid being contained in such amounts in said solution that said polymerized material is not precipitated therefrom, and that the solids content of the resulting mixture is from about 6 to 20% by weight, in which layer said polymerized substance has first been precipitated by evaporation substantially only of said solvent, and the final coating has been formed by subsequent evaporation or" said organic liquid.

23, A temperatureeeusitive recording paper consisting essentially of a dark earlier paper base and a coating thereon of a finely divided gray to white precipitate of a polymerized organic substance having a siutering point of from about 80 to 220 C. and being selected from the group consisting of cellulose esters, cellulose ethers, polystyrene, polyvinylacetate, ketone resins, colophony derivatives, formaldehyde resins, polyvinylidene chloride, polyvinyl chloride, polymethacrylate, coumarone resins and polyisobutylene; said coating having a thickness of at least about 10 to 15 microns, and being formed from a layer of a mixture of the solution of said polymerized organic substance in an organic solvent therefor having a boiling point lower than the sintering point of said polymerized material, with an organic liquid free from hydroxyl groups which has a boiling point above the boiling point of said organic solvent and below the sintering point of said polymeric material, which is inert toward said paper base, and in which said polymerized material is insoluble, said liquid being contained in such amounts in said solution that said polymerized material is not precipitated therefrom, and that the solids content of the resulting mixture is from about 6to 20% by weight, in which layer said polymerized-substance has first been precipitated by evaporation substantially only of said solvent, and the final coating has been formed by subsequent evaporation of said organic liquid.

24. A temperature-sensitive recording paper consisting essentially of a dark carrier paper base and a coating thereon of a finely divided gray towhite precipitate of a polymerized organic substance having a sintering point of from about 80 to 220 C. and an optical brightener; said coating having a thickness of at least about microns, and being formed from a layer of a mixture of the solution of said polymerized organic substance in an organic solvent therefor having a boiling point lower than the sintering point of said polymerized material, with an organic liquid free from hydroxyl groups which has a boiling point above the boiling point of said Organic solvent and below the sintering point of said polymeric material, which is inert toward said paper base, and in which said polymerized material in insoluble, said liquid being contained in such amounts in said solution that said polymerized material is not precipitated therefrom, and that the solids content of the resulting mixture is from about 6 to 20% by weight, in which layer said polymerized substance has first been precipitated by evaporation substantially only of said solvent, and the final coating pable of reacting with said oxidizing agent at a temperahas been formed by subsequent evaporation of said organic liquid.

25. A temperaturesensitive recording paper consisting essentially of a dark carrier paper base and a coating thereon of a finely divided gray to white precipitate of a polymerized organic substance having a sintering point of from about 80 to 220 C., an oxidizing agent selected from the group consisting of acid peroxides and peroxyacids, and a reducing amine capable of reacting with said oxidizing agent at a temperature above their melting points with evolution of heat; said coating having a thickness of at least about 10 to 15 microns, and being formed from a layerof a mixture of the solution of said polymerized organic substance in an organic solvent therefor having a boiling point lower than the sintering point of said polymerized material, with an organic liquid free from hydroxyl groups which has a boiling point above the boiling point of said organic solvent and below the sintering point of said polymeric material, which is inert toward said paper base, and in which said polymerized material is insoluble, said liquid being contained in such amounts in said solution that said polymerized material is not precipitated therefrom, and that the solids content of the resulting mixture is from about 6 to 20% by weight, in which layer said polymerized substance has first been precipitated by evaporation substantially only of said solvent, and the final coating has been formed by subsequent evaporation of said organic liquid.

26. A temperature-sensitive recording paper consisting essentially of a dark carrier paper base and a coating thereon of a finely divided gray to white precipitate of a polymerized organic substance having a sintering point of from about 80 to 220 C., an optical brightener, an oxidizing agent selected from the group consisting of acid peroxides and peroxyacids, and a reducing amine cature above their melting points with. evolution of heat; said coating having a thickness of at least about 5 microns, and being formed from a layerof a mixture of the solution of said polymerized organic substance in an organic solvent therefor having a boiling point lower than the sintering point of said polymerized material, with an organic liquid free from hydroxyl groups which has a boil ing point above the boiling point of said organic solvent and below the sintering point of said polymeric material, which is inert'toward said paper base, and in which said polymerized material is insoluble, said liquid being contained in such amounts in said solution that said polymerized material is not precipitated therefrom, and that References Cited in the file of this patent UNITED STATES PATENTS 2,519,660 James jAug. 22, 1950 2,686,676 Rowe et al Aug. 17, 1954 2,739,909 Rosenthal Mar. 27, 1956 2,859,351 Clark et al. Nov. 4, 1958, 

1. A PROCESS FOR MANUFACTURING TEMPERATURE-SENSITIVE RECORDING PAPER HAVING A LIGHT-COLORED COATING LAYER ON A DARK CARRIER PAPER BASE, COMPRISING ADMIXING WITH THE SOLUTION OF A POLYMERIZED ORGANIC SUBSTANCE HAVING A SINTERING POINT OF FROM ABOUT 80* TO 220*C. IN AN ORGANIC SOLVENT THEREFOR HAVING A BOILING POINT LOWER THAN THE SINTERING POINT OF SAID POLYMERIZED MATERIAL, AN ORGANIC LIQUID FREE FROM HYDROXYL GROUPS WHICH HAS A BOILING POINT ABOVE THE BOILING POINT OF SAID ORGANIC SOLVENT AND BELOW THE SINTERING POINT OF SAID POLYMERIC MATERIAL, WHICH IS INERT TOWARD SAID PAPER BASE, AND IN WHICH SAID POLYMERIZED MATERIAL IS INSOLUBLE, SAID LIQUID BEING ADDED IN SUCH AMOUNTS TO SAID SOLUTION THAT SAID POLYMERIZED MATERIAL IS NOT PRECIPITATED THEREFROM, AND THAT THE SOLIDS CONTENT OF THE RESULTING MIXTURE IS FROM ABOUT 6 TO 20% BY WEIGHT; APPLYING SAID RESULTING MIXTURE ON SAID PAPER BASE; HEATING THE RESULTING LAYER OF SAID MIXTURE ON SAID PAPER BASE TO EVAPORATE SUBSTANTIALLY EXCLUSIVELY SAID SOLVENT THEREFROM, THEREBY FORMING A FINELY DIVIDED GRAY TO WHITE PRECIPITATE OF SAID POLYMERIZED SUBSTANCE IN SAID INERT LIQUID ON SAID PAPER BASE; AND THEN HEATING FURTHER TO SUCH TEMPERATURE AS TO EVAPORATE SAID INERT LIQUID THEREFROM AND FORMING A GRAY TO WHITE COATING OF SAID POLYMERIZED SUBSTANCE ON SAID PAPER BASE. 